1. Field of the Invention
The present invention relates to blood flow measurement by thermodilution measurement, and more particularly to compensating for an injectate induced thermal effect on a thermal sensor in a retrograde catheter.
2. Description of Related Art
In native A-V fistulae, any stenosis is often located at the arterial portion of the vascular access or A-V shunt. The existence of a stenosis in the vascular access typically requires intervention to restore sufficient flow, or at least reduce the rate of occlusion. A typical interventional procedure is angioplasty.
The purpose of the interventional procedures, such as angioplasty, is to restore the flow through the vessel. Interventional radiologists and cardiologists therefore have a need to measure the efficacy of the flow restoring procedure.
In the angioplasty procedure, an interventional radiologist will insert a sheath (introducer) for the angioplasty balloon catheter facing the stenosis location and thus facing the blood flow in the vessel such as an A-V shunt. It is procedurally convenient to use the same introducer (sheath) for flow measurement. This procedure will locate the thermodilution catheter facing the blood flow and the position, facing the flow, is termed as “retrograde” position. Also in clinical situations such as angioplasty of extremities, it is convenient to reach the stenosis location from a downstream cannulation site. In all these situations, the thermodilution catheter will be facing the flow, and thus in a retrograde position. Yet, there remains a need for determining the blood flow rate.
Another situation is related to the endovascular procedure of placement of transjugular intrahepatic portosystemic shunts (TIPS). During the TIPS procedure, a special shunt is created to connect the portal vein with hepatic vein. The TIPS procedure is usually done to decrease the portal hypertension. However, the amount of blood that is taken by the shunt is unknown. If the amount of blood flow through the shunt is too high, then the amount of blood passing through the liver to be filtered is too small, which can result in damage to the patient. Alternatively, if the amount of blood flowing through the shunt and thus shunted from the liver, is small, then the effectiveness of the procedure is diminished. The need exists for determining the blood flow so that proper treatment can be administered.
Currently, blood flow measurements are performed not during intervention but later using color Doppler measurements of line velocity, but do not provide a blood flow measurement in ml/min.
Not withstanding, no practical, relatively quick, and low cost solution exists in the prior art for determining the relevant flow in these example procedures. Therefore, the need exists to measure blood flow using a catheter introduced into the vessel in retrograde direction. It is an object of the present invention to provide low cost flow measurement methods and devices for such measurements which solve the problems (and design constrains) of the retrograde thermodilution catheter.